[PATCH v4 00/16] Initial Prefixed Instruction support

[Nicholas Piggin]

Jordan Niethe's on March 24, 2020 12:54 pm:
> On Mon, Mar 23, 2020 at 9:21 PM Nicholas Piggin <npiggin at gmail.com> wrote:
>>
>> Jordan Niethe's on March 23, 2020 7:25 pm:
>> > On Mon, Mar 23, 2020 at 5:22 PM Nicholas Piggin <npiggin at gmail.com> wrote:
>> >>
>> >> Jordan Niethe's on March 20, 2020 3:17 pm:
>> >> > A future revision of the ISA will introduce prefixed instructions. A
>> >> > prefixed instruction is composed of a 4-byte prefix followed by a
>> >> > 4-byte suffix.
>> >> >
>> >> > All prefixes have the major opcode 1. A prefix will never be a valid
>> >> > word instruction. A suffix may be an existing word instruction or a
>> >> > new instruction.
>> >> >
>> >> > This series enables prefixed instructions and extends the instruction
>> >> > emulation to support them. Then the places where prefixed instructions
>> >> > might need to be emulated are updated.
>> >> >
>> >> > The series is based on top of:
>> >> > https://patchwork.ozlabs.org/patch/1232619/ as this will effect
>> >> > kprobes.
>> >> >
>> >> > v4 is based on feedback from Nick Piggins, Christophe Leroy and Daniel Axtens.
>> >> > The major changes:
>> >> >     - Move xmon breakpoints from data section to text section
>> >> >     - Introduce a data type for instructions on powerpc
>> >>
>> >> Thanks for doing this, looks like a lot of work, I hope it works out :)
>> >>
>> > Yes it did end up touching a lot of places. I started thinking that
>> > that maybe it would be simpler to just use a u64 instead of the struct
>> > for  instructions.
>> > If we always keep the word instruction / prefix in the lower bytes,
>> > all of the current masking should still work and we can use operators
>> > again instead of ppc_inst_equal(), etc.
>>
>> Yeah.. I think now that you've done it, I prefer it this way.
> Sorry, just to be clear which way do you mean?

With the struct, not u64 scalar. mpe's preferred way is fine by me.

>> We'll want to adopt some convention for displaying prefixed
>> instruction bytes, but I don't know what what works best. I wonder
>> if binutils or any userspace tools have a convention.
> binutils-gdb upstream has supports disassembling prefixed instructions.
> Here is what objdump looks like:
>   44:    00 00 00 60     nop
>   48:    00 00 00 07     pnop
>   4c:    00 00 00 00
>   50:    01 00 20 39     li      r9,1
>   54:    00 00 00 06     paddi   r4,r9,3
>   58:    03 00 89 38
>   5c:    00 00 62 3c     addis   r3,r2,0
>>
>> Which reminds me, you might have missed show_instructions()?
>> Although maybe you don't need that until we start using them in
>> the kernel.
> You are right I missed that here.

So binutils doesn't do anything special, I guess you can make something
up.

Thanks,
Nick